This invention relates generally to irrigation sprinklers of the impact or reaction drive types, and more particularly, to a method and apparatus for enhancing the distribution of water from such sprinklers when operated at low pressures.
As is well known in the art, it is highly desirable for each impact or reaction driven sprinkler in a system to provide an even distribution of water over its entire range of throw. Toward this end, it is important that the stream of water emitted by the sprinkler be comprised of at least some droplets of a very small size which will tend to fall out of the stream at a relatively short distance from the sprinkler. Slightly larger droplets fall out of the stream at a greater distance from the sprinkler. Accordingly, by controlling the droplet sizes emitted by the sprinkler, the distribution over the entire range of the sprinkler can be controlled.
One way this has been accomplished is by providing water to the sprinklers at relatively high pressures so the sprinklers produce a spray of water consisting of droplets of relatively small size. Typically, for a given sprinkler and nozzle size, there is a minimum pressure above which water must be supplied to the sprinkler to achieve satisfactory water distribution and sprinkler operation.
By way of example, as shown in the 1977--1978 Irrigation Equipment Catalog published by Rain Bird Sprinkler Mfg. Corp. of Glendora, Calif., for a full circle Model 30 sprinkler with a nozzle size of 3/16 inch, a minimum supply pressure of 45 pounds per square inch (psi) is required to achieve satisfactory water distribution and sprinkler operation. If the pressure is allowed to fall below this required level, the droplet size of the spray increases dramatically, and the distribution pattern will deteriorate appreciably.
When the spray is comprised of large droplets, a high percentage of the water is concentrated at the outer edges of the spray pattern, and when the large droplets fall to the ground, they tend to pack the soil, thereby decreasing its permeability to water. This decreased permeability causes loss of water from run off and evaporation before the water can be absorbed into the soil.
Another method which has been attempted for achieving the desired distribution of water is by ejecting the stream through a non-circular orifice mounted on the sprinkler. In this way, a secondary flow is created within the stream which forms a number of fins of fine spray breaking away from the main stream of water ejected from the sprinkler.
This phenomenon was reported in an article by W. A. Hall and P. A. Boving entitled "Non-Circular Orifices For Sprinkler Irrigation", published in the January, 1956 edition of Agricultural Engineering. Hall and Boving formed the non-circular orifice in an 0.015 inch thick brass ring held in a conventional ring clamp mounted at the end of a sprinkler discharge tube. Although some desirable effects were observed, it was reported that at a relatively low pressure, practically zero fall out occured over about the first one-quarter of the range of the sprinkler. When higher pressure was employed, and undesirable susceptibility to wind drift was observed.
The work of Hall and Boving was expanded upon and further reported in a doctoral thesis submitted to the Department of Agricultural Engineering at Michigan State University in 1956 by Walter K. Bilanski. In that thesis, Bilanski concluded that an equilateral triangular orifice produced the best distribution results when the length of the triangular conduit leading to the orifice extended for a considerable depth into the nozzle. It is believed that the relatively long non-circular passage was required in order to develop a substantial secondary flow within the stream. Although the non-circular orifices described by Bilanski produced the desired distribution of water, the relatively long, straight, non-circular passage creates a significant pressure drop in the nozzle, and it is therefore necessary to supply the irrigation water at a relatively high pressure for proper operation of the sprinkler.
It will be appreciated that large amounts of energy are required to maintain the supply pressure necessary for proper operation of the above described sprinklers. In the well known pivot move type sprinkler systems, for example, it is often necessary to provide high capacity supply pumps typically run by natural gas or electricity, and often even booster pumps along the supply line in order to maintain the required pressure. The cost of the energy consumed by high capacity supply pumps, in addition to the booster pumps, significantly increases the cost of operating such sprinkler systems.
Accordingly, there exists a need for a convenient, effective and economical device for enhancing the water distribution from sprinklers which is capable of operating at energy saving low pressures. As will become apparent from the following, the present invention satisfies that need.